Along with defining consent as a "free agreement", the commission has put forward a list of scenarios where permission has not been given.

It also proposed new offences of sexual assault and sexual coercion, but decided against dropping the need for corroboration in rape cases.

The review follows claims that as few as one in eight victims actually report sex attacks, while recent figures show that 4% of alleged rapes which are reported to the police lead to a conviction.

Professor Gerry Maher, the lead commissioner on the project, said there was no one explanation for the low conviction rate.

But he claimed that offering a legal definition of consent will help override the preconceptions of jurors.

Conviction rates

He added: "We hope that by the law setting out clearly what is and what is not consent, then a jury could not bring their own attitudes about consenting sexual behaviour to the decision making.

"They would have to apply the law as it will become.

"If it is the case that one of the factors that explains conviction rates is social attitudes, then if you change social attitudes then clearly that would have an impact on conviction rates."

The "non-exhaustive" list put forward by the report defining when consent has not been given contains seven different situations.

Today's report brings us a significant step closer to achieving what I hope will be widely-welcomed reforms to benefit both the victims of sexual crimes

Kenny MacAskillJustice secretary

These include when a person is unconscious or asleep, when they agreed under threat of violence, are held captive or deceived about what is happening.

Permission is also not given when a person agrees because the accused impersonated someone known by the victim or when agreement was made by a third party.

It also includes when a person has taken too much alcohol or drugs to be capable of consenting, unless permission was given earlier.

Prof Maher stressed the need for the law to recognise equally male and female victims of rape and sexual assault.

Justice Secretary Kenny MacAskill acknowledged there had been considerable public, professional and academic concern that the current law on rape was unsatisfactory.

He said a consultation would be held on the commission's findings and that a bill would be brought forward by next May.

Mr MacAskill said: "Today's report brings us a significant step closer to achieving what I hope will be widely-welcomed reforms to benefit both the victims of sexual crimes - some of society's most vulnerable individuals - and society as a whole."